High-speed printer having controlled acceleration ribbon positioning differential mechanism

ABSTRACT

A high-speed printer is described which employs a character impression forming ribbon that traverses across a printing area and is selectably movable to permit character impression and subsequent visibility of the character formed. The high-speed printer utilizes a pair of pivoted cantilever arms, one mounted on each side of the printing area. Ribbon guides are mounted adjacent the end of each of the cantilever arms, and the character impression forming ribbon is supported between the two guides across the width of the printing area. A controlled acceleration three-position ribbon raising and lowering differential mechanism is provided for simultaneously raising and lowering the cantilever arms whereby the ribbon is selectively moved as a relatively rigid beam between either of two printing positions or the viewing position by pivotal raising and lowering movement of the cantilever arms. The ribbon raising and lowering means comprises controlled acceleration cam-driven means that operates through a suitable cam follower and linkage arrangement to pivot the cantilever arms in a manner to shift the ribbon from a nonprinting viewing position to a nonviewing printing position and return. The high-speed printer further includes a number of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer. The character impression forming hammers are selectively moved by a drive mechanism that is independently driven with respect to the controlled acceleration drive means for raising and lowering the cantilever arms.

United States Patent [72] Inventor Donald G. Hebert Rochester, NY. [211 App]. No. 734,469

[22] Filed [45] Patented [73] Assignee June 4, 1968 June 8, 1971 General Electric Company [54] HIGH-SPEED PRINTER HAVING CONTROLLED ACCELERATION RIBBON POSITIONING DIFFERENTIAL MECHANISM 17 Claims, 4 Drawing Figs.

51 lnt.CI ..B4lj33/04, B41j33/14 so FieldolSearch 101/96RC,

96,93 RC, 109,l1l,l02,100,336;197/l51, 154, 155,160-165 COLOR ELECTROMAGNET CONTROL Primary Examiner-William B. Penn Arrorneys- Lawrence G, Norris, Michael Masnik, Stanley C.

Corwin, Frank L. Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: A high-speed printer is described which employs a character impression forming ribbon that traverses across a printing area and is selectably movable to permit character impression and subsequent visibility of the character formed. The high-speed printer utilizes a pair of pivoted cantilever arms, one mounted on each side of the printing area. Ribbon guides are mounted adjacent the end of each of the cantilever arms, and the character impression forming ribbon is supported between the two guides across the width of the printing area. A controlled acceleration three-position ribbon raising and lowering differential mechanism is provided for simultaneously raising and lowering the cantilever arms whereby the ribbon is selectively moved as a relatively rigid beam between either of two printing positions or the viewing position by pivotal raising and lowering movement of the cantilever arms. The ribbon raising and lowering means comprises controlled acceleration cam-driven means that operates through a suitable cam follower and linkage arrangement to pivot the cantilever arms in a manner to shift the ribbon from a nonprinting viewing position to a nonviewing printing position and return. The high-speed printer further includes a number of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer. The character impression forming hammers are selectively moved by a drive mechanism that is independently driven with respect to the controlled acceleration drive means for raising and lowering the cantilever arms.

82 HAMMER DRIVE cmcun' PATENTEU JUN 8 IBYI 3583315 SHEET 2 [1F 2 2 52 53 TROL RIBB IF HIGH-SPEED PRINTER HAVING CONTROLLED ACCELERATION RIBBON POSITIONING DIFFERENTIAL MECHANISM BACKGROUND OF INVENTION 1. Field of Invention This invention relates to high-speed printers and to printing ribbon positioning mechanisms therefor.

More particularly, the invention relates to high-speed printers of the type employing a character impression forming ribbon traversed across a printing area and selectively moved up and down to permit character impression on a recording medium and subsequent visibility ofthe character formed.

2. Description of Prior Art High-speed printers of the type employed for use as remote terminal printers for computer readout, or the like, generally utilize electromechanically actuated ribbon positioning mechanisms for moving an inked printing ribbon between a viewing position and a printing position and return. The printing ribbon normally is held in a lowered position to permit visibility of a line being printed when no printing action is required, and selectively is raised to either a black or red ink printing position (if multicolored printing is provided) upon receipt of a printout signal. In such high-speed printers, particularly those employing an array of discrete printing hammers, the ribbon must extend unsupported across the length of the writing area, which in most cases is approximately l7 to inches. Also the ribbon must be readily replaceable by an operator of the equipment, hence the ribbon spoolers must be supported at the sides of the printer in a readily accessible manner. These requirements dictate that ribbon guides be located on the sides of the high-speed printer, and that the ribbon be maintained under tension to give rigidity to the unsupported ribbon section extending across the width of the writing area in order that the ribbon may be raised and lowered as a relatively rigid beam. Further, because of the limited time available in a high-speed printer to raise the ribbon when a print signal is received, and because ofthe requirements previously mentioned above, it is not possible to utilize known raising and lowering mechanisms of the type employed in conventional typewriters wherein ribbon motion is mechanically associated with the typewriter hammer motion. To overcome this difficulty, the present invention was devised.

SUMMARY OF INVENTION It is therefore a primary object of the invention to provide a new and improved high-speed printer having a separate, controlled acceleration, three-position ribbon raising and lowering differential mechanism for raising and lowering the character forming ribbon of a high-speed printer as a rigid beam in a manner which prevents the unsupported ribbon from overshooting the print position.

Another object of the invention is to provide means for preventing overrunning of the ribbon during return movement thereby avoiding undesired noise, bounce and chatter.

A still further object of the invention is the provision of a high-speed printer wherein the printing ribbon is selectively raised or lowered in the above-mentioned manner by appropriate energization of respective raise and lower electromagnets, and selectively may be raised to either one of two different printing'positions to provide multicolor character impression, etc.,.by appropriate energization of a third electromagnet.

In practicing the invention, a high-speed printer is provided which employs a character impression forming ribbon traversing across a printing area with the ribbon being selectively movable topermit character impression and subsequent visibility of the character formed. The high-speed printer includes a pair of pivoted cantilever arms, one mounted on each side of the printing area, and a ribbon guide mounted adjacent the end of each of the pivoted cantilever arms with the printing ribbon being supported between the two guides across the width of the printing area. Controlled acceleration three-position' ribbon raising and lowering means is provided for selectively raising and lowering the cantilever arms whereby the ribbon is selectively moved as a relatively rigid beam between the printing and viewing positions by pivotal raising and lowering movement of the cantilever arms. The ribbon raising and lowering means comprises selectively engageable drive means such as a rotating drive shaft for providing the driving power to raise and lower the cantilever arms and thereby shift the ribbon from a nonprinting viewing position to a nonviewing printing position and return. The raising and lowering means further include cam means of predetermined shape selectively rotatable by the selectively engageable drive means together with cam follower means driven by the cam means. Suitable linkage means intercouple the cam follower means to at least one ofthe cantilever arms for pivoting the same in response to rotation of the cam means and a rotatable shaft interconnects both cantilever arms so that rotation of one of the cantilever arms by the linkage means results in corresponding movement of the other cantilever arm whereby the two cantilever arms pivot in unison.

The high-speed printer further includes a number of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer. The character impression forming hammers are selectively moved by a drive mechanism that is independently driven with respect to the selectively engageable drive means for raising and lowering the cantilever arms. The high-speed printer also further includes means for restraining the return movement of the pivoted cantilever arms to the quiescent viewing position to coincide with rotation of the cam means by the drive means whereby undesired bounce or chatter during or at the end of the return movement is avoided. The high-speed printer also includes interposer means acting on the linkage means to cause the linkage means to increase the angular pivotal movement of the cantilever arms and thereby change the nature of the character impression formed by the ribbon by placing a different portion of the ribbon in the printing position. This different portion of the ribbon may be of a different color, such as red for example, as opposed to a black printing portion which normally would be positioned in the printing location upon the ribbon being raised by the cantilever arms.

BRIEF DESCRIPTION OF DRAWINGS Other objects, features, and many of the attendant advantages of this invention will be appreciated more readily as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, wherein like parts in each of the several figures are identified by the same reference character, and wherein:

FIG. I is an overall, partially disassembled perspective view of a high-speed printer including a controlled acceleration, three-position ribbon raising and lowering differential mechanism constructed in accordance with the invention;

FIG. 2 is a sectional view of a portion of the controlled acceleration differential mechanism comprising a part of the invention taken through shaft 32 and its associated parts;

FIG. 3 is a side view of a portion of the high-speed printer looking in through plane 3-3 and illustrates in further detail the nature of the connecting linkage between the controlled acceleration cam and the pivotally moved cantilever arms for raising and lowering the printing ribbon as a relatively rigid means; and

FIG. 4 illustrates details of the clutch and associated electromagnets used in the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FIG. I of the drawings is a partially broken-away, perspective view of a high-speed printer constructed in accordance with the invention. In the high-speed printer shown in FIG. I, a tworcolor inked ribbon shown at 11 is supported between a pair of cantilever arms 12 and [3 for traversal across a point line generally prescribed by a cylindrical platen shown at 14. The ribbon 11 is comprised by an upper black portion and a lower red portion so that by appropriate positioning, a desired colored character can be printed on a recording medium I (shown in section form) disposed over the platen 14 in back of ribbon ll. Immediately in front ofthe ribbon 11, a high-speed rotating belt 15 of flexible fingers 16, is positioned to rotate the several fingers 16 past the printing area formed by the surface of platen 14 immediately back of ribbon 11 in a sequential known manner. The fingers 16 each have a known character such as one of the letters of the alphabet, punctuation mark, number, etc., formed thereon which are scanned past the front of the ribbon 11 at a known rate. At an appropriate point along the printing area where it is desired to form one of the characters on a recording medium disposed over the platen 14, a selectively operated hammer indicated schematically at 17 is actuated to cause the desired finger 16 to be pressed against the recording medium by way of the inked ribbon 11. The result is to form an inked impression of the character appearing on the selected finger l6 which the hammer l7 actuated.

The hammer 17 is designed to be positioned between the two sides of the rotating belt 15, and is selectively actuated by an electromagnet 18 connected to a lever arm of the hammer 17. Upon energization of the electromagnet 18 from hammer drive circuit, 82, the hammer 17 will be caused to come into contact with a desired selected finger 16 in the abovedescribed manner through the medium of appropriate synchronizing circuitry (not shown) for assuring that hammer 17 when energized by a readout signal to be printed, can be actuated only when the selected character of one of the fingers 16 is properly disposed in front of the hammer. The details of construction of the rotating belt of printing fingers 16, the printing hammer l7, and the required synchronizing circuitry to not comprise a part of this invention. Further details of a preferred arrangement, if desired, may be obtained by reference to copending application Ser. No. 734,501 entitled PRINT ACTUATION SYSTEM, filed June 4, 1968 for Clifford M. Jones and Earle B. McDowell, and assigned to the common assignee. It might also be noted that the invention herein described need not necessarily be employed in conjunction with the particular high-speed printing arrangement depicted in FIG. I, but could also be employed with separately actuated hammers having desired characters formed on their face similar to the arrangements used in conventional typewriters, etc.

The cantilever arms 12 and 13, which support the ribbon ll, each have a vertically supported ribbon guide shown at 21 and 22 rotatably secured on the ends thereof with the ribbon 11 extending between the two guides'and twisted as shown at 23 to extend back over a pair of direction changing guides, one of which is shown at 24 backdown to takeup and payout spools, one of which is shown at 25. The ribbon 11 is caused to be paid out or taken up by either one of the spools 25 through the medium of a suitable ribbon transport mechanism (not shown), and is tensioned so that the portion of the ribbon 11 extending between the two upright guides 21 and 22 across the printing area defined by the surface of the platen 14, is supported as a relatively rigid beam. The cantilever arms 12 and 13 are normally positioned in a quiescent lower position so that characters printed on a recording medium disposed over the surface ofthe platen l4 can be viewed after printing. This occurs as a result of the design of the belt of printing fingers 16 which have adequate spacing between each finger so that as the fingers rotate or move past the printing surface at a high speed, the characters printed on the recording medium can be viewed.

During the printing operation as described briefly above, it is necessary to raise the ribbon 11 so as to place it between a desired selected one of the printing fingers l6 and the recording medium on the surface of the platen 14. Due to the highspeed character of the printer, it is essential that the required raising and lowering of the ribbon ll be conducted separately from the mechanism used to actuate the printing hammers 17 since there is insufficient time between receipt ofa signal that identifies a character to be printed out and the actual printing. to utilize a single mechanism to accomplish both functions in the manner generally employed in conventional typewriters. ln addition, due to the fact that a multicolor ribbon 11 is preferably employed, it is essential that there be no vibration at the end ofthe movement ofthe ribbon 11 into printing position, otherwise a misprint might occur. For this reason, it is necessary to provide a smoothly accelerated raising movement of the ribbon into printing position which will not result in bounce or chatter of the ribbon upon termination of its movement. Similarly, it is desired on the return movement of the ribbon backdown to its quiescent lower viewing position, that no bounce or chatter of the ribbon occur in order to minimize wear and tear ofthe parts, noise, etc.

For the purpose of properly placing the ribbon 11 in printing position with minimum bounce and chatter, a controlled acceleration three-position ribbon raising and lowering differential mechanism is provided by the invention for simultaneously raising and lowering both cantilever arms as a unit in a manner such that the ribbon I1 is selectively moved as a relatively rigid beam between the printing and viewing posi tions. This is accomplished through a pivotal raising and lowering movement of the cantilever arms about a pivot axis shown at 30 through the medium of a rotatable shaft 31. Pivotal raising and lowering of the cantilever arms 12 and 13 about the pivot axis 30 results in a raising and lowering of the ribbon ll as a rigid beam from a nonprinting lower viewing position to a nonviewing upper printing position and return.

The controlled acceleration three-position ribbon raising and lowering differential mechanism is comprised by selectively engageable drive means in the form ofa constant speed rotating drive shaft shown at 32 which is driven by a pulley wheel 33 that is in turn belt driven from a primary drive motor (not shown). The selectively engageable drive shaft 32 is designed to selectively rotate a cam 34 of predetermined shape which in turn drives a cam follower 35. The cam follower 35 is connected through suitable linkage indicated generally at 36 to at least the cantilever arm 13 for pivoting the cantilever arm 13 in response to rotation of the cam 34 by the drive shaft 32. The rotatable shaft 31 is rigidly connected through suitable crank arms to both of the cantilever arms 13 and 12 so that by rotation of shaft 31 both cantilever arms 13 and 12 are pivotally rotated in unison, thereby causing the ribbon 11 to be moved as a beam. The manner in which the several elements of the ribbon raising and lowering mechanism operate will be described in greater detail hereinafter.

The selectively engageable drive means for rotating cam 34 is illustrated in greater detail in H6. 2 ofthe drawing wherein the constant speed rotating shaft 32 is shown in cross section along with the drive pulley wheel 33. The drive shaft 32 includes an integral hub portion 41 which has an inwardly turned flange that abuts against and is in alignment with a cylindrical sleeve 42. The sleeve 42 has the cam 34 keyed to it so that when sleeve 42 rotates, the cam 34 rotates. Sleeve 42 is in rotational sliding contact relationship with an inner pedestal support 43 that is secured to a mounting plate 44 forming a part of the chassis for the high-speed printer. The inner pedestal 43 has a pair of journal bearings 45 and 46 secured therein forjournaling the constant speed rotating shaft 32. As a consequence of this arrangement, the constant speed rotating shaft 32 and its integral hub 41 is free to rotate within the journal bearing 45 and 46 at a constant speed. Under normal quiescent conditions with no printout signal being received, the sleeve 42 will remain stationary along with the inner pedestal support 43 by reason of an auxiliary wrap spring clutch 47 which serves to couple the sleeve 42 to the inner pedestal support 43 and prevent its rotation by reason of any frictional driving tendency on the part of the integral, inwardly turned flange portion 41 of the rotating shaft.

In order to impart a rotational movement to the cam 34, clutch means are provided which in part include the auxiliary wrap spring clutch 47; The clutch means, however, comprises in the main a selectively actuable wrap spring clutch 48 having an outwardly extending actuating arm 49. As will be described more fully hereinafter, the outwardly extending actuating arm 49 normally is engaged by a holding tab when the ribbon is in its quiescent lower viewing position and the wrap spring clutch 48 is in a released condition. In the released condition, the wrap spring clutch 48 allows relative rotation between the integral, inwardly turned flange portion 41. and the sleeve 42. However, when the actuating arm 49 is released from its hold ing tab, the wrap spring clutch functions in a normal manner to firmly grip both the integral, inwardly turned flange portion 41 of shaft 32 and sleeve 42 so as to rigidly couple these two members together. This gripping action on the part of the clutch 48 upon release of its actuating arm 49 is an inherent characteristic of the clutch. For a more detailed description of wrap spring clutches and their characteristics, reference is made to an article entitled Basic Design of Spring Clutches by V. W. Rudnickas and R. A. Fine appearing in Machine Design magazine, May 13, 1965 issue at pages 182-]86.

Upon wrap spring clutch 48 being actuated by release ofthe actuating arm 49 from a holding tab, sleeve 42 will be rotated synchronously with the rotating shaft 32, thereby causing the cam 34 to be rotated. The direction of rotation of sleeve 42 by drive shaft 32 is counter to the main gripping action of the auxiliary wrap spring clutch 47, so that the auxiliary wrap spring clutch 47 releases sleeve 42 and allows it to rotate with hub portion 41 of shaft 32. Thereafter, upon the actuating arm 49 of the wrap spring clutch 48 again coming into contact with a holding tab, the wrap spring clutch 48 will be released and the gripping action of the auxiliary wrap spring clutch 47 will be sufficient to withstand or overcome any frictional driving tendency of the flange 41 to thereby prevent further rotation ofthe sleeve 42 and hence cam 34.

Referring now to FIG. 1 of the drawings, it will be seen that the actuating arm 49 of wrap spring clutch 48 is under the control ofa pair of holding tabs 51 and 52 comprising a part of a movable armature 53. The movable armature 53 is in turn controlled by respective raise and lower electromagnets 54 and 55. Actuation ofthe raise electromagnet 54 in response to energizing signals from 83 will cause the armature 53 to position the holding tab 51 out of engagement with the actuating arm 49 of wrap spring clutch 48. This action is best seen in FIGS. 3 and 4 of the drawings wherein it will be seen that the tab 51 will be moved from the solid-line to the dotted line position, hence releasing the actuating arm 49. The holding tab 52 correspondingly will be moved from its solid-line position to its dotted line position. As a consequence, the wrap spring clutch 48 will be actuated sufficiently to allow the cam 34 to be rotated through approximately 180 where the actuating arm 49 again becomes engaged by the holding tab 52, thereby releasing wrap spring clutch 48 and disconnecting the cam 34 from drive shaft 32. To avoid the necessity of having to continuously energize the raise and lower electromagnets 54 and 55, an overcenter spring 56 is provided which will serve to hold the armature 53 in either the raise position or the lower position, depending upon which electromagnet 54 or 55 has been last energized by 83.

As best shown in H0. 3, upon rotation of the cam 34 from its solid-line position through approximately 180, the cam follower 35 will be driven outwardly from its position shown in H6. 3. The cam follower 35 is rotatably secured on an elongated cam following lever arm 61 at a somewhat central location and is movable with the lever arm 61. The lever arm 61 is pivotally secured to a first elongated connecting link 62 at a point in juxtaposition to the centrally located cam follower 35. The first connecting link 62 is loosely pivotally secured to the pin 64 secured to the mounting plate 44. The remaining end 65 of first connecting link 62 is pivotally secured to a second connecting link 66 that has its remaining end pivotally secured to a crank arm 67 that is fixed to the rotatable shaft 31. A second set of crank arms 70 connect the rotatable shaft 31 to the cantilever arms 12 and 13 for transmitting rotational movement of shaft 31 into up-or-down pivotal movement of cantilever arms 12 and 13, hence raising or lowering ribbon 11. The end of the crank arm 67 remote from rotatable shaft 31 is secured to a strong return spring 68 for causing a return movement of the connecting links 62 and 66 and lever arm 61 back to the normal quiescent lower viewing position upon cam 34 being rotated back to its return position shown in solid lines.

It will be noted that the end of the elongated cam lever arm 61 on the side thereof to which one end ofthe first connecting line 62 is pivotally secured, is designed to stop against hub 69 which is attached to 62 which pivots about 64 which is attached to 44. Arm 61 stays in contact with 69 under conditions where the remaining opposite end 71 of elongated cam follower lever arm 61 is free to move. As a consequence ofthis arrangement, upon rotation of cam 34 to its raised position, cam follower 35 is moved radially outward carrying with it the elongated cam follower lever arm 61. The cam lever arm 61 will remain in contact with 69 and rotate with 62 about 64 since its remaining end 71 is free to move, thereby causing the first connecting link 62 which is shaped in the form of a bellcrank to pull the second connecting link 66 downward. This in turn pulls the crank arm 67 downward and since 67 is rigidly attached to the rotatable shaft 31, the shaft 31 is caused to rotate. Rotation of the shaft 31 causes the output end of the right and left cantilever arms 12 and 13 to be pivoted upwardly by a fixed angular amount determined by the amount of rotation of the crank arm 67. This results in raising the ribbon 11 as a beam so as to position the black ink upper portion of the ribbon 11 in printing position relative to the platen 14, printing fingers 16, printing hammer 17 and the recording paper (not shown). Rotation of the cantilever arm upward also serves to tension the return spring 68 to thereby condition the mechanism for a return stroke.

Should it be desired to achieve a printout in red ink rather than black, interposer means are provided for acting on the linkage 36 to cause the linkage to increase the angular pivotal movement of the cantilever arms 12 and 13 to thereby present the red portion of the ribbon 11 in printing position adjacent the platen. This interposer means is comprised by a selectively actuable interposer lever arm 72 which is actuated by a third electromagnet 73 in response to energizing signals from color magnet control 84. Upon the interposer lever arm 72 being actuated from its dotted line to its solid-line position shown in FIG. 3, it comes into engagement with the end 71 of the elongated cam follower lever arm 61. This serves to fix the normally free end of elongated cam lever arm 61 in a manner such that upon movement outward of the cam follower 35 by reason of rotation of cam 34 to its raised position, the elongated cam lever arm 61 pivots about the now fixed end 71. This results in increasing the angular pivotal movement of the cantilever arms 12 and 13 due to the fact that the point of connection of the first bellcrank-shaped connecting link 62 is caused to move a greater distance than previously when the elongated lever arm 61 was in contact with 69. As a consequence, the stroke of the second connecting link 66 is increased, resulting in a greater angular rotation of the crank arm 67, and hence a greater angular pivotal movement of the cantilever arms 12 and 13.

Lowering of the ribbon 11 from either the black or red printing position, is accomplished by energizing the lower electromagnet 55. Energization of electromagnet 55 causes the armature 53 to be attracted back to its solidline position shown in FIGS. 3 and 4 where it becomes held by the overcenter spring 56. Upon movement of the armature 53 to its lower or return position, tab 52 moves outwardly, thereby releasing the actuating arm 49 of wrap spring clutch 48. This allows the wrap spring clutch 48 to couple drive cam 34 to the constant speed rotating shaft 32 through the medium of sleeve 42 in the previously described manner. Thereafter the drive cam 34 is rotated through approximately 180 until the actuating arm 49 again comes into engagement with the tab 51 ofarmature 53. At this point, the wrap spring clutch 48 is again released, thereby holding cam 34 in the solid-line down or lower position shown in FlGS. 3 and 4. The action of the return spring 68 on the linkage connected to cam follower 35 then assures that theconnecting links 62 and and lever arm 6] follow the movement of cam 34 to its lower position and results in returning the two cantilever arms 12 and I3 along with ribbon 11 to their downward or lower position under controlled acceleration conditions which cushion the return.

During return, the return spring 68 through the cam follower 35 imparts considerable load to the cam 34. This load, due to the inherent inability of the unidirectional wrap spring clutch 48 to resist overrunning, could cause the cam 34 to accelerate and overrun the constant speed drive shaft 32, thereby permitting the cam wrap 35 to return at a much greater rate than is desirable, and possibly result in bounce or chatter of ribbon 11 during its return movement. To prevent this overrunning tendency, a separate, counter action wrap spring clutch 81 (best seen in FIG. 2) is provided. This second wrap spring clutch 81 is mounted internally of the sleeve 42 and the integral inwardly turned flange portion 41 of shaft 32. Thus, if there is any tendency for the cam 34 and hence sleeve 42 to overrun shaft 32, the second wrap spring clutch 81 which acts counter to the first wrap spring clutch 48, operates to effectively maintain the coupling between flange portion 41 and sleeve 42. This results in effectively governing the rotational speed of cam 34 relative to the input shaft 32 and to cushion the return movement.

With cam 34 rotated to the lower position as shown in solid lines in FIG. 3, the actuating arm 49 of wrap spring clutch 48 will be engaged by the tab 51 of armature 53. This results in releasing the wrap spring clutch 48 so that thereafter the integral inwardly turned flange portion 41 of shaft 32 is free to rotate relative to sleeve 42, and hence cam 34. In this situa tion, the gripping action ofthe auxiliary wrap spring clutch 47 is adequate to maintain sleeve 42 and hence cam 34 in place, and hence assures that the wrap spring clutch 48 is maintained in a disengaged position. The use of the auxiliary wrap spring clutch 47 avoids the need of the usual check pawl mechanism generally employed for such purpose and which is costlier, noisier and somewhat position sensitive.

From the foregoing description, it will be appreciated that the invention provides a new and improved high-speed printer having separate, controlled acceleration means for raising and lowering the character forming ribbon of the high-speed printer in a manner which prevents the unsupported ribbon from overshooting the print position. Further, the controlled acceleration three-positioned ribbon raising and lowering differential mechanism also includes means for preventing overrunning of the ribbon during the return movement, thereby avoiding any undesired bounce or chatter at the lower position. Additionally, the ribbon may selectively be raised or lowered by appropriate energization of respective raise and lower electromagnets, and if desired, the ribbon may selectively be raised to either one of two printing positions to provide multicolor or other characteristics to the impressions formed by the ribbon by appropriate energization of a third electromagnet.

Having described a preferred embodiment ofa new and improved high-speed printer having a controlled acceleration three-position ribbon raising and lowering differential mechanism constructed in accordance with the invention, it is believed obvious that other modifications and variations of the invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the preferred embodiment of the invention as described, which changes are within the full intended scope of the invention as defined by the appended claims.

What l claim as new and desired to be secured by Letters Patent of the United States is:

I. In a printer'for printing over a printing ribbon along a print line on a record medium, an arrangement comprising a pair of pivoted cantilever arms each having a respective ribbon guide at its free end and being pivoted at the other end about a common pivot axis, said ribbon guides being positioned at the respective sides of said print line such that a ribbon supported between said guides lies along said print line. means for raising and lowering a ribbon supported between said guides and along said print line as a relatively rigid beam between a printing position and a different position for viewing what has been printed comprising drive means, cam means, cam follower means, means for operating said drive means to rotate said cam means about an axis, linkage means intercoupling said cam follower means to at least one of said cantilever arms, said linkage means responsive to cam follower movement responding to cam rotation about its axis for causing movement of at least one cantilever arm about said common pivot axis. and means intercoupling the two cantilever arms whereby pivotal movement ofone of the arms about said common pivot axis results in a corresponding movement of the other about said common pivot axis in a manner such that the two cantilever arms pivot in unison.

2. A high-speed printer according to claim 1 wherein the means intercoupling the two cantilever arms comprises a rotatable shaft rigidly connected to both said cantilever arms and coupled to and selectively rotated by said linkage means.

3. A high-speed printer according to claim 1 further including a plurality of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer, said character impression forming hammers being selectively moved by a drive mechanism that it independently driven with respect to the drive means for raising and lowering the cantilever arms.

4. A high-speed printer according to claim 2 wherein said drive means comprises a constant speed rotating drive shaft and clutch means for selectively coupling the cam means to the drive shaft.

5. A high-speed printer according to claim 4 wherein the clutch means comprises a wrap spring clutch for selectively intercoupling the drive shaft and the cam means.

6. A high-speed printer according to claim 5 further including a selectively movable armature member having a pair of spaced-apart respective raise and lower tabs for selectively engaging the wrap spring clutch to cause the clutch to intercouplc the drive shaft to the cam means upon release of the wrap spring clutch from either one of the tabs and to release the drive shaft from the cam means upon engagement by either one of the tabs, and selectively operable respective raise and lower electromagnet means for positioning the movable armature member to cause a respective raise and lower tab to selectively engage the wrap spring clutch.

7. A high-speed printer according to claim 6 further including overcenter spring means acting on said armature member for holding the member in either the raise or lower position after placement by the raise and lower electromagnet means.

8. A high-speed printer according to claim 7 further including return spring means acting on at least one ofthe cantilever arms for restoring the ribbon to its viewing position after placement in the printing position, and second wrap spring clutch means operable in a direction counter to that of the first-mentioned wrap spring clutch means for further intercoupling the cam means to the drive shaft during return movement of the cantilever arms and preventing overrunning of the drive shaft by the cam means.

9. A high-speed printer according to claim 11 wherein said interposer means comprises a selectively actuable interposer lever arm for engaging said linkage means to cause the same to increase its stroke and thereby increase the angular pivotal movement of the cantilever arms, and selectively operable electromagnet means acting on said interposer lever arm for selectively actuating the same.

10. A high-speed printer according to claim 8 further including interposer means acting on said linkage means to cause said linkage means to increase the angular pivotal movement'of said cantilever arms and thereby change the nature of the character impression formed by the ribbon.

11. A high-speed printer according to claim 1 further including means for changing the color ofthe character impression formed by the ribbon comprising interposer means acting on said linkage means to cause said linkage means to increase the angular pivotal movement of said cantilever arms and expose a portion ofthe ribbon having a different color.

12. A high-speed printer according to claim 10 wherein said interposer means comprises a selectively actuable interposer lever arm for engaging said linkage means to cause the same to increase its stroke and thereby increase the angular pivotal movement of the cantilever arms, and third selectively operable electromagnet means acting on said interposer lever arm for selectively actuating the same.

13. A high-speed printer according to claim 11 wherein said linkage means comprises an elongated cam follower lever arm having the cam follower means centrally disposed thereon and movable therewith, a first elongated connecting link having a first end pivotally secured to one side of the first cam follower lever arm adjacent the cam follower means and having its central portion loosely pivotally secured to a mounting plate, a second connecting link, and a shaft crank arm secured to the rotatable shaft for the cantilever arms, the connecting link being interconnected between the second end ofthe first elon gated connecting link and the shaft crank arm for rotating the rotatable shaft in response to movement of said cam follower means by said cam means, the elongated cam follower lever arm having the end of the side thereof to which the first elongated connecting link is pivotally secured engageable with a stopping pin secured to the mounting plate under conditions where the remaining end of the elongated cam follower lever arm is normally free to move whereby the cam follower means during rotation of the cam means pivots the elongated cam follower lever arm about the stopping pin and results in a first angular pivotal movement ofthe cantilever arms.

14. A high-speed printer according to claim 13 wherein the interposer means upon actuation serves to fix the normally free remaining end of the elongated cam lever arm in a manner such that upon movement of the cam follower means due to rotation of the cam means the elongated cam lever arm pivots about the fixed normally free end and results in increasing the angular pivotal movement of the cantilever arms.

15. A high-speed printer according to claim 14 wherein said interposer means comprises a selectively actuable interposer lever arm for engaging the normally free remaining end of the elongated lever arm to cause the same to increase the movement of the side thereof to which the first elongated connecting link is pivotally connected to thereby increase the pivotal angular movement of the cantilever arms, and third selectively operable electromagnet means acting one said interposer lever am for selectively actuating the same.

16. A high-speed printer according to claim 15 further including a plurality of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer, said character impression forming hammers being selectively moved by a drive mechanism that is driven independently of the operation of said drive means for raising and lowering the cantilever arms.

17. In a printer, a platen roll for feeding and supporting a recording medium in positionon the platen roll for printing thereon, printing means having type faces which can be positioned to confront said recording medium on the platen roll for printing thereon along a print line and over a two-color printing ribbon interposed between said type faces and said recording medium, ribbon feeding means for feeding said ribbon between said positioned type faces and said recording medium, ribbon-shifting means for shifting said ribbon in a transverse direction relative to said positioned type faces printing means for causing relative prlnting movement of said type faces and said platen roll, said ribbon-shifting means comprising two cantilever arms positioned at the respective sides of said print line and each having a respective ribbon guide thereon for guiding a printing ribbon along a straight path between the platen roll and the positioned type faces, each cantilever arm having its respective ribbon guide at its free end and being pivoted at the other end about a common pivot axis whereby said ribbon guides are rotatable about said common pivot axis, means for positioning a ribbon supported between said guide means as a relatively rigid beam in the transverse width direction of the ribbon between a first color printing position on said ribbon, a second color printing position on said ribbon, and a third nonprinting position for viewing what has been printed comprising means for causing said cantilever arms to rotate simultaneously about said common pivot axis to first, second and third angular positions respectively. 

1. In a printer for printing over a printing ribbon along a print line on a record medium, an arrangement comprising a pair of pivoted cantilever arms each having a respective ribbon guide at its free end and being pivoted at the other end about a common pivot axis, said ribbon guides being positioned at the respective sides of said print line such that a ribbon supported between said guides lies along said print line, means for raising and lowering a ribbon supported between said guides and along said print line as a relatively rigid beam between a printing position and a different position for viewing what has been printed comprising drive means, cam means, cam follower means, means for operating said drive means to rotate said cam means about an axis, linkage means intercoupling said cam follower means to at least one of said cantilever arms, said linkage means responsive to cam follower movement responding to cam rotation about its axis for causing movement of at least one cantilever arm about said common pivot axis. and means intercoupling the two cantilever arms whereby pivotal movement of one of the arms about said common pivot axis results in a corresponding movement of the other about said common pivot axis in a manner such that the two cantilever arms pivot in unison.
 2. A high-speed printer according to claim 1 wherein the means intercoupling the two cantilever arms comprises a rotatable shaft rigidly connected to both said cantilever arms and coupled to and selectively rotated by said linkage means.
 3. A high-speed printer according to claim 1 further including a plurality of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer, said character impression forming hammers being selectively moved by a drive mechanism that it independently driven with respect to the drive means for raising and lowering the cantilever arms.
 4. A high-speed printer according to claim 2 wherein said drive means comprises a constant speed rotating drive shaft and clutch means for selectively coupling the cam means to the drive shaft.
 5. A high-speed printer according to claim 4 wherein the clutch means comprises a wrap spring clutch for selectively intercoupling the drive shaft and the cam means.
 6. A high-speed printer according to claim 5 further including a selectively movable armature member having a pair of spaced-apart respective raise and lower tabs for selectively engaging the wrap spring clutch to cause the clutch to intercouple the drive shaft to the cam means upon release of the wrap spring clutch from either one of the tabs and to release the drive shaft from the cam means upon engagement by either one of the tabs, and selectively operable respective raise and lower electromagnet means for positioning the movable armature member to cause a respective raise and lower tab to selectively engage the wrap spring clutch.
 7. A high-speed printer according to claim 6 further including overcenter spring means acting on said armature member for holding the member in either the raise or lower position after placement by the raise and lower electromagnet means.
 8. A high-speed printer according to claim 7 further including return spring means acting on at least one of the cantilever arms for restoring the ribbon to its viewing position after placement in the printing position, and second wrap spring clutch means operable in a direction counter to that of the first-mentioned wrap spring clutch means for further intercoupling the cam means to the drive shaft during return movement of the cantilever arms and preventing overrunning of the drive shaft by the cam means.
 9. A high-speed printer according to claim 11 wherein said interposer means comprises a selectively actuable interposer lever arm for engaGing said linkage means to cause the same to increase its stroke and thereby increase the angular pivotal movement of the cantilever arms, and selectively operable electromagnet means acting on said interposer lever arm for selectively actuating the same.
 10. A high-speed printer according to claim 8 further including interposer means acting on said linkage means to cause said linkage means to increase the angular pivotal movement of said cantilever arms and thereby change the nature of the character impression formed by the ribbon.
 11. A high-speed printer according to claim 1 further including means for changing the color of the character impression formed by the ribbon comprising interposer means acting on said linkage means to cause said linkage means to increase the angular pivotal movement of said cantilever arms and expose a portion of the ribbon having a different color.
 12. A high-speed printer according to claim 10 wherein said interposer means comprises a selectively actuable interposer lever arm for engaging said linkage means to cause the same to increase its stroke and thereby increase the angular pivotal movement of the cantilever arms, and third selectively operable electromagnet means acting on said interposer lever arm for selectively actuating the same.
 13. A high-speed printer according to claim 11 wherein said linkage means comprises an elongated cam follower lever arm having the cam follower means centrally disposed thereon and movable therewith, a first elongated connecting link having a first end pivotally secured to one side of the first cam follower lever arm adjacent the cam follower means and having its central portion loosely pivotally secured to a mounting plate, a second connecting link, and a shaft crank arm secured to the rotatable shaft for the cantilever arms, the connecting link being interconnected between the second end of the first elongated connecting link and the shaft crank arm for rotating the rotatable shaft in response to movement of said cam follower means by said cam means, the elongated cam follower lever arm having the end of the side thereof to which the first elongated connecting link is pivotally secured engageable with a stopping pin secured to the mounting plate under conditions where the remaining end of the elongated cam follower lever arm is normally free to move whereby the cam follower means during rotation of the cam means pivots the elongated cam follower lever arm about the stopping pin and results in a first angular pivotal movement of the cantilever arms.
 14. A high-speed printer according to claim 13 wherein the interposer means upon actuation serves to fix the normally free remaining end of the elongated cam lever arm in a manner such that upon movement of the cam follower means due to rotation of the cam means the elongated cam lever arm pivots about the fixed normally free end and results in increasing the angular pivotal movement of the cantilever arms.
 15. A high-speed printer according to claim 14 wherein said interposer means comprises a selectively actuable interposer lever arm for engaging the normally free remaining end of the elongated lever arm to cause the same to increase the movement of the side thereof to which the first elongated connecting link is pivotally connected to thereby increase the pivotal angular movement of the cantilever arms, and third selectively operable electromagnet means acting one said interposer lever arm for selectively actuating the same.
 16. A high-speed printer according to claim 15 further including a plurality of character impression forming hammers for selectively engaging the ribbon at desired points to form character impressions on a recording medium supported on the printer, said character impression forming hammers being selectively moved by a drive mechanism that is driven independently of the operation of said drive means for raising and lowering the cantilever arms.
 17. In a printer, a platen roll for feeding and supporting a recording Medium in position on the platen roll for printing thereon, printing means having type faces which can be positioned to confront said recording medium on the platen roll for printing thereon along a print line and over a two-color printing ribbon interposed between said type faces and said recording medium, ribbon feeding means for feeding said ribbon between said positioned type faces and said recording medium, ribbon-shifting means for shifting said ribbon in a transverse direction relative to said positioned type faces, printing means for causing relative printing movement of said type faces and said platen roll, said ribbon-shifting means comprising two cantilever arms positioned at the respective sides of said print line and each having a respective ribbon guide thereon for guiding a printing ribbon along a straight path between the platen roll and the positioned type faces, each cantilever arm having its respective ribbon guide at its free end and being pivoted at the other end about a common pivot axis whereby said ribbon guides are rotatable about said common pivot axis, means for positioning a ribbon supported between said guide means as a relatively rigid beam in the transverse width direction of the ribbon between a first color printing position on said ribbon, a second color printing position on said ribbon, and a third nonprinting position for viewing what has been printed comprising means for causing said cantilever arms to rotate simultaneously about said common pivot axis to first, second and third angular positions respectively. 